1. Field of the Invention
The present invention relates to an instrument for testing a time multiplexed passenger reading light and flight attendant call control system in a commercial aircraft.
2. Description of the Prior Art
Most commercial aircraft designs employ control systems by means of which seated passengers are able to operate overhead reading lights and indicators for calling flight attendants to their seats. Typically, separate buttons are provided in the arm of each aircraft seat, or in a center console between two seats, to operate individual overhead reading lights and an indicator for attracting flight attendant attention to a seat location.
Originally the passenger controls for lighting and flight attendant calling systems were electrical controls coupled by wires that passed in dedicated fashion from the arm of the aircraft seat, beneath the floor of the aircraft and upwardly into the panel space above the passenger location. The operating signals for each passenger's light and call indicator were therefor independent of signals from any other passenger seat. Accordingly, malfunctions in the passenger reading light and flight attendant calling systems at any passenger location were readily isolated and could be associated without difficulty with the particular seat controls and indicators where the malfunction manifested itself.
With the advent of the large commercial aircraft known as jumbo jetliners, a different type of passenger reading light and flight attendant call control system was implemented. Such jumbo jetliners include the DC-10 airplane manufactured by McDonnell Douglas Corporation of Long Beach, Calif., the model 747 aircraft manufactured by Boeing Aircraft Corporation of Renton, Wsh., the model A300 aircraft manufactured by Airbus Industrie of Toulouse, France, and the model L-1011 aircraft manufactured by Lockheed Aircraft Corporation of Burbank, Calif. In commercial jumbo jetliners the large number of wires necessary to provide dedicated controls for each passenger seat to an individual reading light and a flight attendant indicator at a particular passenger location would have created an inordinately great weight. That is, the weight of the wires necessary to provide separate, individually connected controls for each passenger seat was unacceptably large in an aircraft in which every feasible means of eliminating unnecessary weight must be employed. Accordingly, a multiplexed control system was devised in which reading lamps and flight attendant call indicators and controls at each passenger seat were operated on a time-shared, multiplexing system through a central control known as a section timer.
One such multiplexed control system is manufactured for use in the DC-10 aircraft by Hughes Aircraft Corporation of Irvine, Calif. as the model 1022000 multiplex PE/PS System. The Boeing 747 employs a comparable control system known as the ISC system, manufactured by Instrument Systems Corporation of El Segundo, Calif. A new Boeing model 767 aircraft will employ a Panasonic system manufactured by Matsushita Industries in Osaka, Japan or alternatively a system manufactured by Hamilton Standard, a division of United Technologies.
In the Hughes system several modules of the control are each located in association with the aircraft. A section timer govers operation of the control system within each passenger cabin. Beneath each passenger location, which is a group of two or three seats abreast in a cabin, there is a seat encoder which receives signals from all of the individual passenger controls from the seats at that passenger location, and provides a control signal to the flight attendant call indicator at that passenger location. Above the passenger seats at each passenger location, hidden behind overhead panels, there is an overhead decoder which provides operating control signals to the individual passenger reading lights.
The seat locations within a cabin are organized into left and right-hand columns running the length of the airplane. The seat encoders at the passenger locations in each column are connected in series in a loop to the section timer. Likewise, the overhead decoders at each passenger location in each column are also serially connected in a loop to the section timer in the same serial order as the seat encoders associated with the same passenger locations. The section timer cyclically operates to first interrogate a seat encoder and to receive data therefrom on a seat encoder data bus. The section timer then transmits the data to the associated overhead decoder on an overhead decoder data bus and proceeds to the next passenger location in series. In this way the seat encoders are interrogated and the overhead decoders are actuated in time series multiplexed fashion on common data buses.
While such a multiplexing arrangement reduces the necessary weight for a passenger reading light and flight attendant call control system in an aircraft, the interrelationship and common connections of the plurality of controls and actuating systems presents considerable difficulties in locating and remedying malfunctions. Such difficulties are aggravated in the case of multiple malfunctions. Thus, although the passenger reading light and flight attendant calling control systems provide a comfortable amenity to passengers in jumbo aircraft, they contribute inordinately to flight delays and aircraft down time. Moreover, the conventional techniques of isolating and correcting such malfunctions are extremely labor intensive and require a considerable expenditure of time by skilled technicians in locating and correcting troubles.
It is not at all unusual for aircraft to be grounded for many hours, and sometimes even days while technicians attempt to locate troubles in multiplexed passenger reading light and flight attendant call control systems. Moreover, the difficulties in isolating troubles in such systems leads to a great deal of needless work. It is quite time consuming to remove and lower the overhead panels above the passenger seat locations for access to the overhead decoders. Nevertheless, it is not unusual for it to be necessary to drop the overhead panels at many, and sometimes all passenger locations in order to locate an elusive trouble in the system. The time required to locate and correct problems in this fashion with conventional trouble-shooting equipment is considerable.
Also, although the seat encoders are more easily accessible, they are tied to the emergency oxygen mask supply controls. Each time access to a seat encoder is necessary, Federal Aeronautical Administration regulations require a test drop of all oxygen masks in the cabin affected. The necessary testing for oxygen flow through the masks and restoration of the masks to their concealed positions is extremely time-consuming.
As a result of the considerable difficulties encountered in locating and solving problems in a multiplexed passenger reading light and flight attendant calling systems, there is a tendency among airline personnel to ignore slight malfunctions of that system since such problems do not affect the safety of the aircraft. As a result, problems in the reading light and call control tend to accumulate over a period of time. Eventually, a problem will occur in the system which can no longer be ignored, such as the simultaneous blinking of a number of overhead reading lights, or the failure of any of the reading lights in a loop to respond to actuation of a reading light button by any of the passengers. In such circumstances it is necessary to take the aircraft affected out of service until these problems can be corrected. When such a malfunction reflects an accumulation of problems, however, the situation is frequently one in which multiple problems exist. Since these problems can be located using conventional test equipment only with considerable difficulty, the aircraft is frequently out of service for an extended period of time.